No, history was not rewritten. What the folks there don't seem to want to acknowledge is that GHCN circulates two files, described here. The file everyone there wants to focus on is the adjusted file (QCA). This, as explained, has been homogenized. This is a preparatory step for its use in compiling a global index. It tries to put all stations on the same basis, and also adjust them, if necessary, to be representative of the region. It is not an attempt to modify the historical record.

That record is contained on the other data file distributed - the unadjusted QCU file. This contains records as they were reported initially. It is generally free of any climatological adjustments. For the last 15 or so years, Met stations have submitted monthly CLIMAT forms. You can inspect these online. Data goes straight from these to the QCU file, and will not change unless the Met organisation submits an amended CLIMAT file. This is the history, and no-one is tampering with it.

The adjusted file does change, as the name suggests it may. Recently, it has been modified to use an improved pairwise comparison homogenization algorithm due to Menne and Williams. It is now (as of Dec 15 2011) used by GISS instead of their own homogenization algorithm, which makes the QCA file much more significant.

Update. I have a new post which looks at the GHCN adjustments more generally, with visualization.

The Iceland Met Office record

So Paul raised this with the Icelandic Met Office, with the following loaded questions:a) Were the Iceland Met Office aware that these adjustments are being made?
No we were not aware of this.b) Has the Met Office been advised of the reasons for them?
No, but we are asking for the reasonsc) Does the Met Office accept that their own temperature data is in error, and that the corrections applied by
GHCN are both valid and of the correct value? If so, why?
The GHCN “corrections” are grossly in error in the case of Reykjavik but not quite as bad for the other stations. But we will have a better look. We do not accept these “corrections”.d) Does the Met Office intend to modify their own temperature records in line with GHCN?
No.

And the Met sent their own version of the Reykjavik data. But what is missing from this dialog is that GHCN was never altering their QCU record, and is not suggesting that the Iceland records should be changed. I'll show the QCU data for the period most complained of, post 1939. Units are .01°C. Unfortunately, the Dec numbers got lost in formatting.

Year

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

1937

80

-160

-130

500

690

960

1160

1040

860

400

360

1938

10

180

200

470

600

920

1130

1060

940

490

170

1939

-150

130

360

500

870

1080

1300

1230

1180

740

150

1940

160

170

-20

300

760

970

1120

1010

710

630

130

1941

-30

-150

210

540

880

1150

1230

1150

1150

710

480

1942

160

190

270

360

770

970

1140

1130

790

260

410

1943

40

-90

150

290

500

990

1140

990

810

450

200

1944

-170

60

140

410

660

990

1300

1180

800

460

10

1945

-260

10

410

440

760

980

1190

1200

960

720

650

1946

240

-20

280

320

840

870

1060

1060

800

760

140

1947

320

-200

-280

170

830

990

1090

1100

770

560

30

1948

70

200

320

120

460

940

1060

1100

620

310

250

1949

-270

0

10

0

360

980

1050

1010

900

450

250

1950

280

-70

130

220

710

930

1240

1220

720

450

70

1951

-150

-90

-300

0

690

980

1060

1140

970

570

90

1952

-290

-30

100

340

620

830

1010

1010

760

570

260

1953

60

180

270

10

680

1020

1190

1150

970

420

200

1954

200

10

160

450

760

1020

1060

1100

610

370

270

1955

-200

-270

140

560

570

990

1050

1010

810

390

430

1956

-320

270

360

360

660

840

1070

990

930

470

500

1957

110

-150

40

500

700

990

1200

1130

710

470

300

Despite all the invocation of the Iceland data, there is no electronically readable form supplied. You can compare the link above, though, and you will see that the GHCN QCU data is almost identical. There are changes of a fraction of a degree - the Iceland Met do say that they have also made some adjustments.

Actually there are isolated differences. These seem to be sign differences, where GHCN has a negative sign. The sign may have disappeared in scanning the Iceland numbers.

The story of the Reykjavik adjustments was taken up by Ole Humlun, with again the same disdain for the record contained in the GHCN QCU file and the purpose of the homogenization adjustment. He refers to the Iceland data, and to Rimfrost, but does not mention the almost identical QCU.

The V3.1 adjustments

It is true that the adjustments have changed recently. V3.1 was released 4 November 2011. I have a QCA file from 14 July 2011, and this is, for Reykjavik, almost identical to the QCU file. I have a v2.mean file from Dec 2009, which is the V2 unadjusted file, and it is essentially identical to the current QCU file. In v2 style, it had duplicates. there were four for Reykjavik, but they had little overlap and where they did, were consistent. The unadjusted file has not changed, but the QCA file has.

I also have an adjusted v2 file from Dec 2009. The adjustments are substantial, but less than the current ones.

So here is the plot of the current QCU file vs the adjusted QCA file:

And here is the plot of differences

As you see, the adjustments are substantial. I have done a repeat of the GHCN analysis that we did for Darwin, with a histogram of the effect on trends. I will blog about this shortly. Current estimate is that this adjustment is in the top 10%.

Sunday, January 22, 2012

TempLS showed a very small rise in global mean anomaly in December, from 0.358 °C to 0.364 °C. Now NOAA and GISS are out. NOAA has a slightly larger rise, from 0.437°C to 0.457°C. And GISS has a small fall, from 0.48°C to 0.45°C. All these are relative to their respective base periods. Time series graphs are shown here

As usual, I compare the previously posted TempLS distribution to the GISS plot. Here is GISS:

The dry adiabatic lapse rate (DALR) is in the news again. Willis Eschenbach has led a discussion primarily directed at a theoretical musing on whether gas under gravity but without heat input would have a lapse rate or be isothermal.

I've explained my views on the role of the DALR here and here, and in comments on several other blogs. Just a brief recap of theory; the DALR is the vertical temperature gradient given by:dT/dz = -g/cp = -9.8 °C/km for air,
where z is altitude, g gravity acceleration, and cp is the (constant pressure) specific heat of air. Any gas cools when it expands adiabatically (ie without exchanging heat with the environment). The rate at which dry air cools as it rises (and the pressure falls) is also the DALR.

The air generally does have a lapse rate which is not quite as large as the DALR. This observed rate is called the environmental lapse rate. The difference is often attributed to the effect of water condensation, and there is reference to a moist adiabatic lapse rate. I think that is only part of the story, as I'll show.

But my view of the role of the DALR, and the answer to Willis' query, is fairly simple. Air motions create a heat pump which move temperatures toward the DALR. If you could prevent all motion, conduction would move the temperature gradient to isothermal. But you can't; in practice the air needs heating to keep it from liquefying, and that will always create motion.

In this post, I'll review the heat pump notions, and add an entropy viewpoint which will quantify some of the issues.

The heat pump of moving air.

I've talked about that in the previous posts referenced above. For here, I'll just repeat part of a comment I made at WUWT

When the lapse rate is below the dry adiabat (toward isothermal) it is referred to as convectively stable. Above the adiabat, it is unstable. At the adiabat, it is neutrally stable.

At the adiabat, rising air cools by expansion, at exactly the rate at which the nearby air is becoming cooler (by lapse rate). And falling air warms. There is no buoyancy issue created. Moving air retains the same density as the environment. And no heat is transferred.

But in the stable regime, falling air warms faster than the change in ambient. It becomes less dense, so there is a force opposing its rise. That is why the air is stable. This motion both takes kinetic energy from the air and moves heat downwards (contra your statement). It is a heat pump which works to maintain the lapse rate.

Rising air does the same. It cools faster, and so rises against a buoyancy force. It takes KE from the air and moves “coolness upwards”, ie heat down. It pumps heat just as falling air does.

That is why air in motion tends to the adiabat lapse rate. A heat pump requires energy. Where from?

The atmosphere is famously a heat engine, driven by temperature differences, most notably from equator to pole, but also innumerable local differences, eg land/sea. This provides the kinetic energy that maintains the lapse rate, and it is hard to imagine any planetary atmosphere where the energy would not be available.

The effectiveness of the heat pump tapers as the adiabat lapse rate is approached. Beyond, in the unstable region, everything is reversed. The pump becomes an engine, with heat moving upward creating KE. This of course quickly diminishes the temperature gradient.

Entropy

As said above, a heat pump is needed to maintain a lapse rate. The reason is that there is the irreversible process of conduction down the temperature gradient:

Q = -k ∇T

where k is the thermal conductivity (W/m/°K), and Q is the flux. This is a general Fourier law, and k need not be simply molecular conductivity. For present purposes it is augmented by turbulent transfer and also by radiative transfer if there are GHGs.

I'm using "irreversible" in the thermo sense; heat flow down the gradient can be (and is) reversed by a heat pump. But that takes energy.

Since the Fourier law flow is irreversible, it creates entropy:

dEA/dx = Q d(1/T)/dx, where EA is a time rate of increase of entropy per unit area, or more conveniently (see Eq 3):EV = (k/T2) ∇T • ∇T, where EV is the rate of entropy increase per unit volume.

As you see, EV depends only on k and the temperature and its gradient. It happens inexorably, with or without gravity. You can only reach a steady state if you either

have gradient zero

have k=0 or

use energy to counter the entropy increase

The adiabatic heat pump does counter the entropy increase. But of course, globally entropy grows. The energy for the heat pump comes from air motion created by the global atmospheric heat engine, which necessarily creates at least as much entropy as the heat pump negates. And that entropy is ultimately exported from the Earth.

Environmental lapse rate

The observed lapse rate is usually less than the DALR, and this is often attributed to moisture. There isn't actually a "moist adiabatic lapse rate" that you can cite a value for. But one way of seeing how moisture could matter is if you think of the role of specific heat. This is just the amount of heat needed to change the temperature, and during condensation, you can say that the specific heat experiences a spike - effectively a delta function with area LH. When the SH rises, g/cp diminishes. But the moist adiabat does require that condensation is actually happening, and of course in the air that happens only in some places at some times.

But another reason for the lapse rate falling short of the DALR is simply that the heat pump is inadequate. It's effectiveness tapers to zero as the lapse rate approaches the DALR. But in fact the rate of entropy creation that it has to counter is quite high when GHG are present, because of radiative transfer (Rosseland conduction). And as above, to the extent that it is inadequate, the temp gradient tends toward isothermal.